Really bad stars on 72ED with ASI533MC Pro

No image.

One thing that might help you find out if it's the field flattener causing it is to rotate your flattener 180° and see what happens.

Me thinks it is tilt if the image shown is the full field covered by the 533. As comparison this the equivalent field covered on my ED72 (taken with a Nikon D5100 so 4.78 um pixels):

As can be seen the field should show little field curvature and lateral color. No FF used.

Light_NGC7000_300.0s_Bin1_20230702-003336_0020.jpg

Thanks guys. Here's an outstretched individual sub (Saved as jpeg due to file upload size limit here)

I had one of these and it does suffer from focus tilt
Great scope garbage focuser

I've found the tilt analyser in SIRIL but I'm not sure what I'm looking at and can't find any tutorials. Anyone know what any of this means?

Screenshot 2023-07-05 at 13.32.47.png

I experienced a very similar issue recently. I was getting slightly streaked stars like this (as opposed to oval stars from my reflector's poor collimation).  A clue was that the direction of the streaks were mostly unchanged across the field of view.

But I don't think I was getting the red/blue chroma shift, so maybe my problem is unrelated. 

Nevertheless, here's a summary of my experience—

I stopped a run of subs to investigate, re-homed the scope, and double-checked polar alignment (with iPolar).  The scope had indeed shifted...and not by very much. The "ball" was still on the crosshairs, but shifted to the left about half way. It was re-centered and the subsequent set of subs came out perfectly.

This happens occasionally with my rig. The tripod sits on a dolly, so there's lots of opportunity for something to move after initial PA. Temperature changes, slight weight shift, and tension release can be the culprits. This is despite a nicely balanced system!

The ultimate solution, of course, is a pier. But I would probably run in to it with the car, being in the middle of my driveway and all.

BTW. this is one reason why I would avoid using a strain wave mount without a counterweight on a portable tripod. Shifting forces are significant. Check out an EDGEHD 14" moving about at https://www.highpointscientific.com/ioptron-hem27ec-hybrid-equatorial-mount-head-with-ipolar-and-case-h274a  I don't see the tripod move, but, man, that's a lot of weight shifting!

Craig Dixon:
Light_NGC7000_300.0s_Bin1_20230702-003336_0020.jpg

Thanks guys. Here's an outstretched individual sub (Saved as jpeg due to file upload size limit here)

To me that seems to be tilt. It doesn't look like backspacing otherwise all corners would have equally stretch stars which is not the case. The upper left corner seems to be the worse. I vote for tilt. 
I hope you can fix it.

Quick update here. I purchased and fitted an adapter ring that allows me to attach the FF to the focuser tube via a screw thread rather than via two grub screws in an attempt to reduce/eliminate tilt. Attached is a single auto-stretched sub converted to jpeg. I think the stars look much better. What do we think?

Will have a look at the focussed this week, although it does seem pretty solid

Damien Galanaud:
It looks significantly better with probably still a little bit of tilt. I owned the 72ED which was in fact my first refractor. One issue it has that can significantly contribute to the tilt issue is that the focuser tends to become loose over time, especially if you put in the back end heavy equipment such as flatteners and astro cameras. You can check this by trying to move the draw tube up and down. If you have this issue, you can find tutorials online explaining how to tighten it back.

*1 Thank you i was looking for it